Transporting and storing temperature sensitive cargo over periods of time may require a controlled climate in the space where the cargo is loaded. Climate control includes controlling the temperature of the cargo to be within a certain predefined acceptable range. Controlling the temperature includes bringing the temperature of the cargo into an acceptable range (by refrigerating or heating) and maintaining the temperature within that range. Climate control may also include controlling the humidity of the space where cargo is loaded.
The temperature of temperature sensitive cargo should be kept within predefined acceptable limits. Some cargo must be maintained frozen, and the temperature of any part of the frozen cargo must be kept below a predefined freezing temperature which depends on the cargo, e.g. below 10 degrees Fahrenheit or lower, while commodities such as fresh fruit and vegetables should be kept chilled, but not frozen, to stay fresh.
During operation of a refrigeration system water vapor will condensate on the evaporator and form a layer of ice that will degrade the efficiency of the evaporator and thereby of the refrigeration system. The ice is removed by running a defrosting cycle. Traditionally, defrosting cycles are initiated according to a predetermined schedule at time intervals which may depend on the nature of the cargo and the time since its loading into the container.
Some cargoes need relative humidity to be kept below acceptable upper limits. Some of these cargoes are also sensitive to temperatures, while others are relatively insensitive to temperature. Examples of such products are electronic and optical products, scientific instruments, machinery and metals such as iron and steel that may corrode if the relative humidity is too high, clothing and other textiles where fungus growth can be prevented by keeping the relative humidity low.